Dielectric resonators are widely employed in modern microwave communication systems, because of their compactness and superior performance in terms of Q-factor and temperature stability. Most common dielectric-loaded cavity filters employ high permittivity cylindrical disks (or pucks) suspended within a metallic enclosure and operating in their fundamental TE01δ mode, or in a higher order HE11δ mode. Conventionally, the pucks are axially located along the metallic enclosure, or mounted in a planar configuration, as shown in FIGS. 1A and 1B.
The HE11δ dual-mode resonators allow for compact in-line structures, and are extensively used for satellite applications, in which the number of physical cavities used in a filter structure can be reduced. Pseudoelliptic responses can be obtained by achieving cross-coupling among the modes of adjacent resonators. In particular, the various modes are usually coupled, in order to obtain quadruplets of resonators, thus yielding symmetric responses.
The TE01δ single-mode cross-coupled filters with planar layouts enable extended design flexibility for achieving both symmetric and asymmetric pseudoelliptic responses; they also provide higher spurious performance over dual-mode filters at the expense of size and mass. For these reasons, as well as design simplicity, the TE01δ single-mode cross-coupled filters are among the most common dielectric resonator filters, especially for terrestrial applications. Although the in-line topology is convenient for mechanical and size considerations, TE01δ single-mode filters with in-line structure are not used for applications requiring minimum volume or resonator count, for critical specifications, due to their inability to yield pseudoelliptic responses.
The present invention addresses new configurations of TE01δ single-mode filters that implement pseudoelliptic responses, within an in-line structure. As will be explained, the present invention uses single-mode TE01δ dielectric resonators with different orientations, that are cascaded along an evanescent mode waveguide. Dielectric resonators operating in the higher order TE01(nδ) modes (i.e. nth order harmonic resonances) can be used as well.